Method of attaching or replacing a plug assembly

ABSTRACT

A plug assembly includes a plug stem having a plug stem base, a plug head, and a fastening mechanism for fastening the plug stem base to the plug head, the fastening mechanism comprising at least two retainer clamps that surround and provide an interference fit between the plug stem base and the plug head. A method of replacing or attaching a plug head to a plug stem includes providing a plug stem having a plug stem base, providing a plug head, providing a fastening mechanism comprising at least two retainer clamps, and coupling the fastening mechanism around the plug stem base and the plug head to provide an interference fit between the plug stem base and the plug head.

CROSS-REFERENCE TO RELATED APPLICATION

This application is divisional application of U.S. Pat. No. 8,500,093,filed Jun. 8, 2009, which is a utility conversion of U.S. ProvisionalPatent Application Ser. No. 61/059,682, filed Jun. 6, 2008, for “PLUGASSEMBLY WITH PLUG HEAD ATTACHMENT.”

FIELD OF THE INVENTION

This invention relates to industrial valves. More specifically, thisinvention relates to methods for attaching valve plug heads to valveplug stems.

BACKGROUND OF THE INVENTION

Valves and valve plugs are well known in the art. Typically, valve plugheads are positioned within the valve to control the volume of flowpassing through the valve. By modifying the position of the plug headrelative to the valve seat, control of the flow volume is achieved, thusallowing diversion and restriction of fluid flow. Plug heads aresubjected to fluid forces, chemical attack, thermal stresses, impactfrom particulates and debris, as well as the forces used to attach it tothe plug stem and seat loading forces that can occur when the plug headcomes into contact with the valve seat. The valve head is typicallyattached to a plug stem, which in turn is connected to an actuatingdevice. This actuating device is controlled to move the plug stem, whichacts to change the position of the plug head to control the flow passingthrough the valve.

The plug stem is subjected to axial forces as the actuator moves it,mounting forces relating to the actuator attachment, and the longcylindrical section is subjected to bending forces. The plug head andthe plug stem perform distinctly different purposes and are subjected tovery different forces. The plug head, sitting in the middle of the flowstream, diverts and/or restricts flow, and is subjected to fluid andseat loading forces and to forces related to attaching the plug head tothe plug stem. In contrast, the plug stem is moved by an actuatingdevice to provide a sealing surface and is subject to axial and bendingforces. In industrial, high volume/flow rate valves, the forces placedon plug stems and plug heads are typically significant contributors tovalve failure.

Traditionally, valve plug heads are either composed of one monolithicmaterial or make use of more than one material. Plug heads employingmore than one type of material have particular advantages, inparticular, better erosion and corrosion resistance, improved shockabsorption, working life, and thermal expansion qualities. However, theuse of a plurality of material types has been limited by the ability toeffectively join the materials together economically and withoutcreating stress points that limit the life of the plug head.

The most common methods of fixing dissimilar materials together in avalve plug are taper fitting or interference fitting, both of whichemploy a retaining ring that is fixed around the plug head. Taperfittings have been shown typically to subject the plug head toundesirable stresses, contribute to thermal expansion problems, and aredifficult to repair. The typical taper fitting design requires a matingof two conical surfaces, one on the plug head, and the other on theretaining ring. Since neither the plug head nor the retaining ring canbe manufactured with ideal cone shapes, the plug and seat may not mateperfectly. As such, loading between the two mated structures may not beuniform. Additionally, the force of the retaining ring on the plug headis exerted close to the edge of the plug head and is generallyperpendicular to the angle of the conical surface. The location andangle of the force can introduce undesirable tensile forces into theportion of the plug head that bears the force. Often the desired plughead material may demonstrate weak tensile strength, thus introducingadditional tensile forces that can either limit the selection of plughead materials or that can cause breaking of the edge of the plug head,separating the plug head from the plug stem and causing valve failure.Also, as the retaining ring wears away through normal corrosion anderosion, the shape of the contact area can change, typically movingcloser to the edge of the plug head. This contact area change tends toconcentrate forces on the edge of the plug head and increases thelikelihood that the edge of the plug head will fracture, thereby causingthe plug head to separate from the plug stem. The stresses induced withthe taper fit are difficult to quantify and, therefore, can detract froma valve plug's performance. Variables in the welding process, such asweld shrinkage, inter-pass temperature, amperage of weld, inert gasenvironment, and the amount of initial burn-in, can change the amount ofstress in the plug head.

As noted above, typical prior taper fit designs attach the taper fitring to the plug stem via welding. This approach results in theretaining ring and the plug stem becoming permanently joined into onecomponent. If the plug head wears away or breaks and the plug stem isstill usable, the typical taper fit design does not lend itself toachieving the proper concentricity between the plug head and the plugstem after the plug head has been replaced. When a taper fit valve plugis repaired, the plug stem has already been machined, so it is notpossible to make adjustments in the plug stem to ensure concentricitywith the plug head. If the plug head is misaligned, adjustments cannotbe made without cutting the taper fit ring off. For at least thesereasons, taper fit valve plugs are usually discarded (as opposed tobeing repaired) when the plug head has broken or worn away. Duringassembly, the taper fit ring is typically fit tightly around the ceramicplug and the taper fit ring is welded to the plug stem. At elevatedoperating temperatures, the taper fit ring increases in size more thanthe plug head, and the plug head becomes somewhat loose in the taper fitring, which thereby leads to early failure of the fit in operatingconditions.

Interference fittings typically require a bulkier retaining ring,contributing to the load on the plug head. Interference fittings alsorequire more complex procedures to replace plug heads and are generallylimited in their service temperature ranges. An interference fitachieves more uniform loading of the plug head than does the taper fit.However, the typical interference fit uses a one-piece retaining ringthat not only holds the plug head but also attaches the plughead/retaining ring assembly to the plug stem. The interference fit alsomust have sufficient material to allow for the wear due to erosion andcorrosion without causing the plug head to separate from the plug stem.These requirements result in a bulkier retaining ring than is requiredto hold the plug head in place, which contributes to an additional loadon the plug head. This additional load introduces tensile stresses,which tend to contribute to plug head breaking and separation, which canresult in valve failure.

Even with interference fit designs, the task of replacing the plug headis quite complex. To replace the plug head, the interference fit ringmust be cut, separating the plug head and ring assembly from the plugstem. This process is usually performed on a lathe or mill. If the ringis to be used again, it is necessary to separate the ring from the plughead. Certain combinations of plug head and interference fit ringmaterials can be separated by heating the assembly in an industrialoven. If the coefficient of thermal expansion of the retaining ring issufficiently higher than the plug head, the retaining ring will expandmore quickly and the interference fit will be negated as a space faunsbetween the two surfaces. This approach is somewhat destructive andrequires that the interference-fit ring be carefully checked beforereuse. Also, this heating method only works with certain combinations ofmaterials. Moreover, even when it may work, the plug head replacementprocess requires specialized manufacturing facilities that are generallyunavailable to users in remote locations. Therefore, replacing plugheads for valve plugs is not a typical industry practice for certaincombinations of materials or user locations.

Another problem with interference fittings is that service temperatureranges are limited because of differential thermal expansion between theplug head and ring materials. The amount of interference between theplug head and the ring is directly related to the amount of stress in aplug head. The amount of interference at ambient temperature becomes aconcern when it places large amounts of stress on the plug head. Thus,when the valve plug is installed and is warming to operatingtemperature, the plug head is more highly stressed and is morevulnerable to failure. It has also been observed that because of thesestresses, certain valve plugs, head and rings, could not be used becausethe ambient temperatures, or below ambient storage temperatures, couldcause the plug head to fail before they could placed into service.

Also, both taper fittings and interference fittings suffer from theimpracticalities of stress relieving heat affected weld zones with heattreatments. For highly corrosive fluid applications and with certainmaterials, it is important to stress relieve heat affected weld zoneswith heat treatments. With both prior existing taper fit andinterference fit designs, this has not been considered practical becausestress-relieving typically is performed at temperatures high enough toallow the plug head to be excessively loose in the ring, and it is notpossible to assure that the plug head would return to its properposition upon cooling. Therefore, even though heat treatments might bebeneficial, they have generally been avoided.

In view of the foregoing shortcomings, it would be desirable to providea valve plug design that uses a clamping system to attach the valve plughead to its valve plug stem, and to thereby provide a means ofassembling and replacing worn plug heads in the field, while allowinguse of different materials for the plug head and the plug stem, wherethe different materials are selected specifically to address thedifferent function of the plug head and the plug stem. This type of plugdesign is particularly desirable for use in flow streams that areerosive or corrosive in nature, because plug heads in these kinds ofstreams typically suffer material loss due to the erosion and/orcorrosion and require regular replacement. Often the plug head wears outbefore other valve components. Therefore, minimizing the occurrenceswhen the plug head fails and must be replaced is very desirable inimproving the life cycle and efficiency of the valve.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a side view of a plug head and a plug stem accordingto an embodiment of the present invention;

FIG. 2 illustrates an enlarged view of clamps, plug stem, and plug headaccording to an embodiment of the invention;

FIG. 3 illustrates an enlarged side view of a plug head and a plug stemaccording to an embodiment of the present invention;

FIG. 4 illustrates a representative system of a valve plug according toan embodiment of the present invention in a valve assembly; and

FIG. 5 illustrates a section view of a valve plug having a plug headmounted to plug stem base of a plug stem according to an embodiment ofthe invention.

SUMMARY OF THE INVENTION

One embodiment of the present invention includes attaching a ceramic (orother sacrificial material) plug head to a plug stem. The embodimentuses two retainer half rings (clamps) and two or more bolts/nuts to holdthe head onto the plug stem. In this fashion, replacement of the plughead can be easily and quickly accomplished in the field. The two clampsare configured such that a gap is left therebetween on both sides. Thebolts/nuts are sacrificial bolts which are inexpensive. Rather than undothe bolting, these bolts can easily be cut off and thrown away. Thebolting can then be replaced and a new plug head installed, reusing allof the major components. Other embodiments may use three or moreretainer rings (clamps) to hold the plug head onto the plug stem. It isunderstood that all modifications and embodiments discussed herein mayalso be adapted to include three or more retainer rings (clamps).

When ceramic plugs are used, it is common to replace field worn plugheads with new ones. These applications often involve scaling, erosionand high temperatures. This design has several advantages over currentdesigns. This design is easier to work on in the field and the factory.Assembly of this design is simpler than previous designs. Some olddesigns even required shrink fitting and welding of the parts to holdthem together. This precluded field assembly of plugs. This designallows simple field assembly. Assembly in the factory is alsosimplified. The gap left between the two clamps is important as many ofthe services which require erosion-resistant plug heads have solids inthe fluid stream. Solids tend to build up on parts. When threaded partsare used it can make undoing threads impractical or impossible, whichwould make reusing the stem impossible.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present invention includes a plug assembly thatincludes a plug head made of a sacrificial material that is attached toa plug stem with two retainer half rings. The plug assemblies of thisinvention are adapted for use in industries such as, for example,mining, chemical processing, and oil and gas refining, where the flow isabrasive and/or corrosive and which may contain substantial quantitiesof sediment, debris or scale. Valves in certain erosive and/or corrosiveflow streams encounter a significant amount of sediment, debris or scalewhich comes through the pipe line. This invention provides plug headsand stems being made of dissimilar materials having different propertiesthat optimize the performance of the plug head, the plug stem and thefastening band. Also, this invention is adapted to ease the process ofrepair and replacement of valve plug components, permitting maintenanceto be accomplished in the field without requiring specializedmanufacturing equipment or highly skilled personnel. The invention isalso adapted to provide a tight shutoff by permitting improved alignmentof the plug head and seat ring.

In a particular embodiment of the invention, the plug assembly allowsthe plug head to shift from side to side. When control valves areproduced, there is always a certain amount of variation in the parts andassembly. However, in order to provide tight shutoff, the plug head andseat ring must line up perfectly. Since manufacturers cannot make theparts perfectly, plug assemblies need a certain amount of adjustability.

In most valves, the seat ring can shift a little from side to side toallow the seat ring to center up on the plug. This is typically done bykeeping the bonnet a little loose while stroking the plug into the seatrepeatedly. Once the seat ring has moved to center itself, the bonnet isthen tightened, locking the seat into place. This process is describedin detail in the Mark One User Manual (VLENIM0001) steps 7.9 to 7.9.2,the contents of which are incorporated by reference herein. Some valvedesigns allow the bonnet to shift a little from side to side instead ofshifting the seat ring, as when a screwed in seat is used. In the caseof survivor, the seat ring is pinched between the valve outlet and thevalve body. Performing a seat centering procedure is more difficult andis described in the Survivor User Manual (VLENIM0036), the contents ofwhich are incorporated by reference herein.

Because this process is so difficult to perform, one particularembodiment of the present assembly is configured to allow the plug headto float (instead of the bonnet or seat ring). This particularembodiment allows the plug head to move slightly from side to side. Thisaction allows the plug head to find a natural center on the seat ring,providing the best shutoff possible.

Referring to FIGS. 1 and 3, a particular embodiment of the plug head andplug stem of the present invention is illustrated. A valve plug 100 isshown having a plug head 101 held in a plug stem base 103 which in turnis mounted on the plug stem 102. As shown in FIG. 2, the plug head 101includes a base portion with a beveled edge 110. A distal portion of theplug stem 102 includes a beveled edge 112. The plug head 101 is held inthe plug stem base 103 by two clamps (half rings) 104 which provide aninterference fit between the plug head 101 and the plug stem 102. Thetwo clamps 104 are fitted over the plug head 101 and the plug stem base103 and are tightly held in place by four bolts 120. In a particularembodiment of the invention, the bolts 120 are fixed in place by nuts107 a, 107 b. Alternatively, two clamps can be held in place by pins,screws, welds, brazing, clamps or the equivalent. Additionally, theclamps 104 can include a hinge mechanism or tongue-and-groove mechanismto hold the two clamps 104 together on one end, while relying on twobolts 120 to secure the two clamps 104 together at an opposing end. Thetwo clamps 104 can provide shock absorbing capabilities and stressrelief to the plug head 101 during use.

The preferred plug head 101 can be composed of structural ceramicsbecause of its resistance to wear and degradation in flow streams thatare erosive (having fine-grit particles) and corrosive (due to thechemical composition of the flow). Structural ceramics are a class ofmaterials that includes, but is not limited to silicon carbide, siliconnitride, aluminum oxide, zirconium oxide, tungsten carbide,whisker-reinforced blends of ceramics, two-phase ceramics, and the like.Alternative materials which may be substituted for structural ceramicsfor the plug head 101, include, but are not necessarily limited to,cermets, which are compounds that are combinations of ceramics andmetals, cast iron, silicon iron, white iron, heat treated martensiticsteels (such as 440 or 416 grade steel), CrCoFe alloys (such asSTELLITE® alloy 3, STELLITE® alloy 6, and STELLITE® 12), or othermetals. Alternative materials with similar properties can be substitutedwithout departing from the concept of this invention.

The plug stem 102, plug stem base 103 and clamps 104 can be composed ofmaterials selected for ease of machining to a smooth surface, havinggood tensile strength, reasonable ductility and cost effectiveness.Included within this class of materials are titanium and its alloys,zirconium and its alloys, niobium and its alloys, titanium-niobiumalloys, alloy steels, carbon steels, —iron-based superalloys, stainlesssteels, nickel and its alloys, —nickel-based superalloys, copper-basedalloys, cobalt alloys, —cobalt-based superalloys, aluminum and itsalloys, magnesium alloys, tantalum, and the like. Alternative materialswith similar properties can be substituted without departing from theconcept of this invention.

The clamps 104 can be composed of metal alloys, including but notlimited to titanium and its alloys, zirconium and its alloys, niobiumand its alloys, titanium-niobium allows, alloy steels, carbon steels,—iron-based superalloys, stainless steels, nickel and its alloys,—nickel-based superalloys, copper-based alloys, cobalt alloys,—cobalt-based superalloys, aluminum and its alloys, magnesium alloys,tantalum and metals of similar properties. Alternative materials withsimilar properties can be substituted without departing from the conceptof this invention.

FIG. 4 shows a representative system of a valve plug 100 of thisinvention in a valve assembly 300. The valve plug 100 is shown in asubstantially closed position with the plug head 101 closing a firstflow path 303 from the valve chamber 301 and a second flow path 302. Theplug stem 102 is shown connected to the actuator 304 and sealed with theshaft 305 in close, preferably fluid tight proximity, with valve stemsupport (or shaft support) packing (not shown). FIG. 4 shows anembodiment of the valve plug 100 in its working environment in a typicalvalve assembly 300. The actuator 304 functions to position the valveplug 100 either in the shown closed position or retracted to permitfluid flow from the first flow path 303 to the second flow path 302.Alternatively, the flow can, as is common in some valves, flow in theopposite direction.

FIG. 5 shows a section view of an alternative embodiment of a valve plug200 having a plug head 201 mounted to plug stem base 203 of a plug stem202, this embodiment having additional compliance structure provided. Incontrast to the embodiment described in FIG. 1, the present embodimentincludes a plug stem base 203 having a base portion with a non-beveledend or edge 214. Additionally, the plug stem base 203 can have a smallerdiameter than the diameter of the plug head 201. Plug head 201 caninclude a base portion with a beveled edge 210. This design permits theplug head 201 and clamps 204 to move and adjust relative to the plugstem 202, which allows the plug head 201 to self center when in use in avalve assembly, such as the valve assembly 300 of FIG. 4. An embodimentof the valve plug 200 can include washers or springs 220 within oradjacent to plug stem base 203 to provide cushioning and separationbetween the plug stem base 203 and the plug head 201. Representativespacers include, but are not limited to Bellville washers and springmechanisms.

Alternative embodiments of the invention include spacers (not shown) onthe bolt sections between sections of the clamps 204 that are adjacentto plug head 201 in order to prevent deflection of the clamps 204.

The described embodiments, including the various materials, specificcomponents, and dimensions, are to be considered in all respects only asillustrative and not as restrictive. The invention should not beconsidered limited to the particular preferred and alternativeembodiments, rather the scope of the invention is indicated by theappended claims. All changes, modifications and alternatives which comewithin the meaning and range of equivalency of the claims are to beembraced as within their scope.

What is claimed is:
 1. A method of replacing or attaching a plug head toa plug stem comprising: providing a plug stem having a plug stem base, aplug head, and a fastening mechanism for fastening the plug stem base tothe plug head, the fastening mechanism comprising at least two retainerclamps that surround and provide an interference fit between the plugstem base and the plug head; and coupling the fastening mechanism aroundthe plug stem base and the plug head to provide an interference fitbetween the plug stem base and the plug head.
 2. The method of claim 1,further comprising selecting the interconnecting mechanism to comprise asacrificial interconnecting mechanism adapted for destructive removal torelease the plug head from the plug stem base.
 3. The method of claim 2,wherein the sacrificial interconnecting mechanism comprises bolts, pins,screws, welds, brazing, or clamps.
 4. The method of claim 2, furthercomprising cutting the sacrificial interconnecting mechanism.
 5. Themethod of claim 1, wherein the plug stem has a first beveled edge, theplug head has a second beveled edge, the at least two retainer clampssurround and provide an interference fit between the first beveled edgeof the plug stem base and the second beveled edge of the plug head; andfurther comprising an interconnecting mechanism joining the at least tworetainer clamps on at least one end of the at least two retainer clamps,wherein the at least two retainer clamps and the interconnectingmechanism are configured to form at least one gap between a firstretainer clamp of the at least two retainer clamps and an adjacentretainer clamp of the at least two retainer clamps to which the firstretainer clamp is joined, the at least one gap sized and configured toprovide access to the interconnecting mechanism extending between thefirst retainer clamp and the adjacent retainer clamp.
 6. The method ofclaim 1, wherein the fastening mechanism is configured to allow the plughead to move side to side to allow the plug head to find a naturalcenter on a seat clamp.
 7. The method of claim 1, wherein the plug headis made of a sacrificial material configured to be removed from the plugstem base and replaced with another plug head.
 8. The method of claim 1,wherein the at least two retainer clamps are held in place bysacrificial bolts configured for removal from the fastening mechanismand from the plug stem base and replacement with another set ofsacrificial bolts.
 9. The method of claim 8, wherein the sacrificialbolts are held in place by nuts.
 10. The method of claim 1, wherein theat least two retainer clamps are held in place by sacrificial pins,screws, welds, brazing, or clamps.
 11. The method of claim 1, whereinthe fastening mechanism provides shock absorbing capabilities to theplug head.
 12. The method of claim 1, wherein the plug stem comprises atleast one of titanium, zirconium, niobium, alloy steels, carbon steels,iron-based superalloys, stainless steels, nickel, nickel-basedsuperalloys, copper-based alloys, cobalt alloys, cobalt-basedsuperalloys, aluminum, magnesium alloys, tantalum, or any alloysthereof.
 13. The method of claim 1, wherein the plug head comprises atleast one of silicon carbide, silicon nitride, aluminum oxide, zirconiumoxide, tungsten carbide, whisker-reinforced blends of ceramics,two-phase ceramics, and cermets.
 14. The method of claim 1, wherein thefastening mechanism comprises at least one of titanium, zirconium,niobium, alloy steels, carbon steels, iron-based superalloys, stainlesssteels, nickel, nickel-based superalloys, copper-based alloys, cobaltalloys, cobalt-based superalloys, aluminum, magnesium alloys, tantalum,or any alloys thereof.
 15. The method of claim 1, wherein the plug stembase has a smaller diameter than the diameter of the plug head.
 16. Themethod of claim 1, further comprising washers, springs, or clampspositioned within or adjacent to plug stem base to provide cushioningand separation between the plug stem base and the plug head.
 17. Themethod of claim 1, wherein each of the at least two retainer clamps areconfigured to be spaced apart from one another by the interconnectingmechanism.
 18. A method of replacing or attaching a plug head to a plugstem comprising: providing a plug stem having a plug stem base, a plughead, and at least two band sections that surround and provide aninterference fit between the plug stem base and the plug head, the atleast two band sections joined together with and spaced apart by asacrificial interconnecting means; and coupling the at least two bandsections around the plug stem base and the plug head to provide aninterference fit between the plug stem base and the plug head.
 19. Themethod of claim 18, wherein the sacrificial interconnecting means isconfigured for destructive removal from the fastening means and from theplug stem base and replacement with another sacrificial interconnectingmeans.
 20. The method of claim 19, wherein the sacrificialinterconnecting mechanism comprises bolts, pins, screws, welds, brazing,or clamps.
 21. The method of claim 19, further comprising cutting thesacrificial interconnecting mechanism.
 22. The method of claim 19,wherein the plug stem base has a smaller diameter than the diameter ofthe plug head.
 23. The method of claim 19, further comprising washers,springs, or clamps positioned within or adjacent to plug stem base toprovide cushioning and separation between the plug stem base and theplug head.